Title: Electric transport in few-layer TMD back-gated field effect transistors Antonio Di Bartolomeo, PhD Professor: University of Salerno, Italy, Physics Department “E. R. Caianiello” adibartolomeo@unisa.it ABSTRACT: Transition-metal dichalcogenides (TMDs), such as MoS2, WSe2, or PdSe2, have recently become very popular for next-generation electronic devices and sensors as an alternative or a complement to graphene. Such materials offer remarkable properties, which include layer-dependent bandgap, intrinsic n- or p-type conduction, mechanical strength, chemical stability, strong light interaction and high sensitivity to several environmental parameters. Monolayer WSe2 and MoS2 have 1.6-1.8 eV direct bandgap and enable field-effect transistors with high On/Off current ratio and strong photoresponse [1,2]. PdSe2, which is the first isolated TMD with pentagonal structure, has lower indirect bandgap, vanishing with the increasing number of layers, and exhibits ambipolar conduction with tunable n- and p-type conduction. A challenge in the use of these materials is the achievement of high carrier mobility, which typically results in the order of few tens cm2V-1s-1, and is dramatically affected by oxygen, water or other adsorbates and process residues [3]. Here, we discuss the current-voltage characteristics at high drain bias of monolayer MoS2 transistors with Schottky contacts [4]. We show that oxidized Ti contacts, due to a long air exposure, form rectifying junctions on MoS2 and cause asymmetric output characteristics, which we explain in terms of two back-to-back Schottky barriers with slightly unbalanced barrier heights. We use MoS2 transistors with ohmic contacts, at lower drain bias, to investigate the photoconductive and photogating effects [1]. We point out that the photoconductivity can persist with a decay time longer than 104 s, due to photo-charge trapping in extrinsic and intrinsic defects. By focusing on the hysteretic behavior of the transistor transfer characteristics, we demonstrate that positive charge trapping is dominant in 2D-materials on SiO2 dielectric and can be used to realize memory devices [5]. We investigate the effect of irradiation by low-energy electrons during the usual SEM imaging and show that its detrimental effect is partially recovered after a long time annealing at room temperature [6]. Taking advantage from the n-type conduction, combined with the low work function and the sharp edge geometry, we demonstrate field emission current from few-layer MoS2 and WSe2, which is promising for vacuum electronic applications [2,6-7]. In particular, we prove that the field emission current from a WSe2 flake can be modulated by a back gate and propose a new field emission transistor [2]. Finally, we show the modulation of the ambipolar conduction in PdSe2 transistors by pressure control [8]. References 1. Di Bartolomeo A et al. (2017) Electrical transport and persistent photoconductivity in monolayer MoS2 phototransistors. Nanotechnology 28:214002, Doi: 10.1088/1361-6528/aa6d98. 2. Di Bartolomeo A et al. (2019) A WSe2 vertical field emission transistor. Nanoscale, 2019, 11, 1538 - 1548. Doi: 10.1039/C8NR09068H 3. Urban F. et al. (2018) Environmental effects on the electrical characteristics of back-gated WSe2 field-effect transistors. Nanomaterials 8: 901. Doi: 10.3390/nano8110901 4. Di Bartolomeo A et al. (2018) Asymmetric Schottky contacts in bilayer MoS2 field effect transistors. Advanced Functional Materials 28: 1800657. Doi: 10.1002/adfm.201800657 5. Di Bartolomeo A et al. (2018) Hysteresis in the transfer characteristics of MoS2 transistors. 2D Materials 5:015014. Doi: 10.1088/2053-1583/aa91a7 6. F. Giubileo et al. (2019) Effect of electron irradiation on the transport and field emission properties of few-layer MoS 2 field effect transistors. J. Phys. Chem. C, 2019, 123 (2), pp 1454–1461 Doi: 10.1021/acs.jpcc.8b09089 7. Urban F et al. (2018) Transport and field emission properties of MoS2 bilayers. Nanomaterials 8:15. Doi: 10.3390/nano8030151151 8. A. Di Bartolomeo et al. Pressure-tunable ambipolar conduction and hysteresis in thin palladium diselenide field effect transistors Advanced Functional Materials, 2019 In Press

Electric transport in few-layer TMD back-gated field effect transistors

Antonio Di Bartolomeo
Writing – Review & Editing
2019-01-01

Abstract

Title: Electric transport in few-layer TMD back-gated field effect transistors Antonio Di Bartolomeo, PhD Professor: University of Salerno, Italy, Physics Department “E. R. Caianiello” adibartolomeo@unisa.it ABSTRACT: Transition-metal dichalcogenides (TMDs), such as MoS2, WSe2, or PdSe2, have recently become very popular for next-generation electronic devices and sensors as an alternative or a complement to graphene. Such materials offer remarkable properties, which include layer-dependent bandgap, intrinsic n- or p-type conduction, mechanical strength, chemical stability, strong light interaction and high sensitivity to several environmental parameters. Monolayer WSe2 and MoS2 have 1.6-1.8 eV direct bandgap and enable field-effect transistors with high On/Off current ratio and strong photoresponse [1,2]. PdSe2, which is the first isolated TMD with pentagonal structure, has lower indirect bandgap, vanishing with the increasing number of layers, and exhibits ambipolar conduction with tunable n- and p-type conduction. A challenge in the use of these materials is the achievement of high carrier mobility, which typically results in the order of few tens cm2V-1s-1, and is dramatically affected by oxygen, water or other adsorbates and process residues [3]. Here, we discuss the current-voltage characteristics at high drain bias of monolayer MoS2 transistors with Schottky contacts [4]. We show that oxidized Ti contacts, due to a long air exposure, form rectifying junctions on MoS2 and cause asymmetric output characteristics, which we explain in terms of two back-to-back Schottky barriers with slightly unbalanced barrier heights. We use MoS2 transistors with ohmic contacts, at lower drain bias, to investigate the photoconductive and photogating effects [1]. We point out that the photoconductivity can persist with a decay time longer than 104 s, due to photo-charge trapping in extrinsic and intrinsic defects. By focusing on the hysteretic behavior of the transistor transfer characteristics, we demonstrate that positive charge trapping is dominant in 2D-materials on SiO2 dielectric and can be used to realize memory devices [5]. We investigate the effect of irradiation by low-energy electrons during the usual SEM imaging and show that its detrimental effect is partially recovered after a long time annealing at room temperature [6]. Taking advantage from the n-type conduction, combined with the low work function and the sharp edge geometry, we demonstrate field emission current from few-layer MoS2 and WSe2, which is promising for vacuum electronic applications [2,6-7]. In particular, we prove that the field emission current from a WSe2 flake can be modulated by a back gate and propose a new field emission transistor [2]. Finally, we show the modulation of the ambipolar conduction in PdSe2 transistors by pressure control [8]. References 1. Di Bartolomeo A et al. (2017) Electrical transport and persistent photoconductivity in monolayer MoS2 phototransistors. Nanotechnology 28:214002, Doi: 10.1088/1361-6528/aa6d98. 2. Di Bartolomeo A et al. (2019) A WSe2 vertical field emission transistor. Nanoscale, 2019, 11, 1538 - 1548. Doi: 10.1039/C8NR09068H 3. Urban F. et al. (2018) Environmental effects on the electrical characteristics of back-gated WSe2 field-effect transistors. Nanomaterials 8: 901. Doi: 10.3390/nano8110901 4. Di Bartolomeo A et al. (2018) Asymmetric Schottky contacts in bilayer MoS2 field effect transistors. Advanced Functional Materials 28: 1800657. Doi: 10.1002/adfm.201800657 5. Di Bartolomeo A et al. (2018) Hysteresis in the transfer characteristics of MoS2 transistors. 2D Materials 5:015014. Doi: 10.1088/2053-1583/aa91a7 6. F. Giubileo et al. (2019) Effect of electron irradiation on the transport and field emission properties of few-layer MoS 2 field effect transistors. J. Phys. Chem. C, 2019, 123 (2), pp 1454–1461 Doi: 10.1021/acs.jpcc.8b09089 7. Urban F et al. (2018) Transport and field emission properties of MoS2 bilayers. Nanomaterials 8:15. Doi: 10.3390/nano8030151151 8. A. Di Bartolomeo et al. Pressure-tunable ambipolar conduction and hysteresis in thin palladium diselenide field effect transistors Advanced Functional Materials, 2019 In Press
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/4730266
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